Study Shows Long-Term Effects Of Diabetes And Prediabetes On The Brain

One of the largest studies on the connection between blood sugar and brain function has found that people with prediabetes and diabetes experience worse long-term cognitive decline than people with normal blood sugar levels. The results underscore just how dangerous impaired blood sugar is for overall health, from heart to brain – but the study also suggests that there’s a possible good news side to this story.

Previous studies have linked diabetes with decreased brain function, but this is the largest to find a direct relationship between A1c blood levels and risk of long-term cognitive decline. The A1c test (referred to as the HbA1c test in this study) reflects average blood sugar for the previous two to three months. Diabetes is generally defined by an A1c level of 6.5% or above, the equivalent of 126 mg of blood sugar per deciliter. A result of between 5.7 and 6.4% is considered prediabetic, which indicates high risk for developing diabetes.

The study involved about 5,000 people in the UK, average age 66 (participants in the English Longitudinal Study of Ageing), including people with normal blood sugar levels and those with levels falling in the prediabetic to diabetic range. Cognitive function was evaluated at the beginning of the study and reassessed every two years over an eight year span to track changes in memory, executive brain function (such as decision-making speed), and overall cognitive function.

The results showed that those with prediabetes or diabetes had significantly decreased cognitive scores over the study period, including memory and processing speed – all signs of more rapid cognitive decline. The results held true even after accounting for factors like smoking, alcohol consumption, cholesterol levels, depression, high blood pressure, and demographics like age, sex and marital status.

The researchers noted that all of the participants experienced some level of cognitive decline (natural result of getting older), but prediabetes and diabetes made the onset of decline come faster and the effects steeper than for people with normal blood sugar.

The really chilling part of these results is less about the effects of diabetes (which are already well evidenced), and more about the effects of being even in the vicinity of diabetes. The study suggests that someone doesn’t have to be diagnosed as officially diabetic to experience worse cognitive decline – falling in the prediabetic range is close enough.

"Our study provides evidence to support the association of diabetes with subsequent cognitive decline. Moreover, our findings show a linear correlation between circulating HbA1c levels and cognitive decline, regardless of diabetic status,” the research team said in the study’s conclusion.

The good news is that getting ahead of blood sugar irregularities earlier could potentially slow the rate of cognitive decline.

“Our findings suggest that interventions that delay diabetes onset, as well as management strategies for blood sugar control, might help alleviate the progression of subsequent cognitive decline over the long-term,” added the researchers.

These results strengthen the argument that we’d do well to take blood sugar seriously and implement changes to manage it, ideally before getting close to the diabetic range -- but even with a diagnosis of diabetes, lifestyle changes can go a long way toward managing it. Dietary changes, exercise, and losing weight have all been shown to influence blood sugar levels. It's doable, and it's one of the few serious risk factors affecting brain function that we can do something about.

David DiSalvo is the author of "Brain Changer: How Harnessing Your Brain’s Power to Adapt Can Change Your Life" and the best-selling "What Makes Your Brain Happy and Why You Should Do the Opposite", which has been published in 13 languages. His work has appeared in Scientif...